1. Field of the Invention
This invention relates to zoom lenses and more particularly to zoom lenses preceded by a lens unit of negative power and haing three lens units in total of which the first two counting from front are axially moved to vary the image magnification. Still more particularly it relates to zoom lenses of reduced size with high zoom ratio.
2. Description of the Prior Art
The zoom lenses for photography which have achieved minimization of the size of lens system in such a manner that the entire system is shortened not only in the longitudinal direction but also in the lateral direction are known, as, for example, disclosed in Japanese Laid-Open Patent Applications Nos. SHO 58-111013, 58-178316, 59-16248 and 59-18917. Any of these zoom lenes is comprised of three lens units of which the first counting from front is of negative power, the second is of positive power, and these two are axially moved to effect zooming.
Of these, Japanese Laid-Open Patent Applications Nos. SHO 58-111013 and 58-178316 have achieved the advance in that respect by taking the so-called 2-unit type zoom lens as the basic configuration, but their zoom lenses having a zoom ratio of a little less than 2 cannot be said to be of high range.
Meanwhile, Japanese Laid-Open Patent Application No. SHO-59-18917 shows a zoom lens whose range begins with a somewhat wide angle, speaking in terms of 35 mm Leica format, 28 mm, while still permitting the range to be extended to as high as three. But, the total length of the entire system is long, and its diameter is large, so that this zoom lens becomes slightly bulkier than the standard.